This invention relates to a technique of recording and reproducing digital patterns as a sound track of a motion picture film.
The sound track of a conventional motion picture film is adapted for optically recording analog audio signals thereon. That is, in a recording/reproducing system for a digital sound track on a motion picture film, as disclosed in JP Patent Kokai-Publication No. 05-40938, provisionally published on Feb. 19, 1993, an analog audio recording track and a digital audio recording track are provided on the motion picture film. Analog audio signals are recorded on or reproduced from the analog audio recording track in accordance with the usual analog recording/reproducing system. On the other hand, high quality digital audio data is generated from the audio information of a particular channel and compressed digital audio data is generated from the audio information of the remaining channels, and each of these digital audio data is recorded on or reproduced from the digital audio recording tracks.
On the other hand, in the recording method as disclosed in JP Patent Kokai-Publication No. 5-109196, provisionally published on Apr. 30, 1993, digital data consisting of a pre-set number of data strings are optically recorded on respective digital audio data recording tracks. Since each 16-bit sample data is recorded in a square 4.times.4 matrix pattern, the rate of data errors along the longitudinal direction of the film is reduced to one-fourth of that when the 16-bit sample data is arrayed longitudinally. The rate of data errors along the width of the film may similarly be reduced as compared to the case in which the sample data is arrayed transversely across 16 tracks.
In contrast to these prior-art techniques, there has also been proposed in International Publication Number WO 92/14239 a motion picture film in which the film area between perforations for film feed is employed as a digital pattern recording region.
For projecting such motion picture film, sound reproduction with rich ambience and with high sound quality is required, while it is necessary to process playback data by error correction or error concealment.
In a digital equipment employing a conventional recording medium, such as a compact disc (CD), error correction is made using the cross-interleaved Reed-Solomon code for protecting data against random or burst errors. The extent of error correction capability is determined depending upon the nature of errors liable to be produced in a particular recording medium.
Meanwhile, the film area reserved for recording the audio signals is susceptible to damages by the film driving system, such that particularly long burst errors tend to be produced with increase in the number of times of film reproducing operations. For this reason, it is necessary to provided a longer interleaving length for eliminating sound interruptions. However, if the interleaving length is increased, phase deviation is incurred between the picture on the film and the audio information thus imposing constraints on the editing by manual film cutting which is the basic film editing technique. Thus there is a certain limitation to increasing the interleaving length.